Atomic particle generating device



May 2, 1961 w. A. HOYER ETAL ATOMIC PARTICLE GENERATING DEVICE Filed March 25, 1959 FIG. 2;

R.F. GENERATOR PULSEI') VOLT SOU INVENTORS. WILMER A. HOYER,

ROBERT C. RUMBLE, w fia M'TORNEY.

Patented May 2, 1961 ice ATOMIC PARTICLE GENERATING DEVICE Wilmer A. Hoyer, Bellaire, and Robert C. Rumble, Houston, Tex., assignors, by mesne assignments, to Jersey Production Research Company, Tulsa, Okla, a corporation of Delaware Filed Mar. 23, 1959, Ser. No.'801,291

9 Claims. (Cl. 250-845) This invention relates'to radiation generating devices, and more particularly to controllable radiation generators adapted for logging boreholes.

There have been devised in the past a number of radiation generators making use of a source of electrically charged particles and a charged particle accelerator for directing said particles at a high velocity against certain targets. When the target material, the type of particle, and the particle velocity at the instant of bombardment are all properly selected, a particular nuclear reaction,

such as the generation of neutrons, may be obtained. For example, deuterium ions directed at a tritium-containin-g targetby a 100 kv. potential source will produce 14 mev. neutrons from the target. Other nuclear reactions may be used to produce neutrons; such reactions are described in U.S. Patent No. 2,816,242Goodman.

Neutron generators of the type described above have become particularly useful in connection with the logging of boreholes. However, generation devices known heretofore have been unduly complex and, as a result, often have given considerable trouble in the field. When a neutron generator is lowered down a borehole, it is almost inevitable that the generator will receive strong shocks and suffer vibrations that may damage the constituent parts thereof sufficiently to produce inoperability. Furthermore, as a result of the great number of electrodes and electrical connections in the devices used heretofore, manufacturing costs and a number of rejects due to improper vacuum seals may be unduly high.

The invention contemplates the use of the type of neutron generator wherein an ionizable gas and a suitable I target are enclosed within a gas-tight housing adapted to be divided into an ionizationcompartment and an ion accelerating compartment. The gas may be ionized by inducing a radio frequency-electromagnetic field within the housing of strength suflicient to produce an ionized gas plasma within the housing. (The word plasma" is used here to describethat state of an ionizedgasin which the concentrationsof negative'and positive charges are almost equal. Reference maybe had to the article Operating Characteristics of a High Yield R.F. Ion

Source, by H. P. Eubank, R. Truel-l, and R. A. Peek, Jr., appearing in Review of Scientific Instruments, vol. 25, No. at pp.-989995,-for a discussion of ionized gas plasma). This may be done by placing a coil around the portion of the housing including the ionization compartment and energizing the coil from a suitable source of radio frequency energy. 1

A source of high voltage pulses is connected between the coil andthe target'to produce an electric field that. vwill attract ions to the target for production of desired radiation; Manifestly, if all of the ions in the plasma ,produced by the radio frequency field are'attracted to p the target simultaneously, the plasma will be extinguished.

Therefore, apartition must be placed. betweenthe ioniza- -Qtion compartment and the targetto keep a'sufli'c'ient num-.

her of ions in the ionization compartment to maintain the plasma.

In accordance with the teachingsof this invention, a porous plate, which may comprise a multiplicity of very small balls of glass or other vitreous material, is used to divide the neutron generator into an ionization compartment and an ion accelerating compartment. Most of the ions that are drawn toward the target strike the sintered glass and ricochet back into the ionization compartment. Some, of the ions, however, find their way along tortuous paths in the interstices within the sintered glass into the ion accelerating compartment Where they are accelerated toward the target. I

Theinvention will be described in more detail with reference to the accompanying drawing, wherein:

Fig. l is a cross-sectional side view of an embodiment of the invention;

Fig. 2 is a schematic diagram of the generating device shown in Fig. l and electrical equipment for controlling the operation of the generator; and

Fig. 3 is a microscopic view of a portion of the sintered glass plate shown in Fig. 1.

The generating device comprises a suitable housing 1 which'rnay be an elongated, gas-tight envelope of glass, boron nitride, quartz, or other suitable nonco-nductive material that does not tend to absorb or adsorb gases. The housing is divided into an ionization compartment 2 and an accelerating gap compartment 14 by a partition comprising a glass neck 5 and a' sintered glass partition 7.

At or near the end of the accelerating gap and facing the ionization compartment is a target member 15. The target member 15 may be recessed to receive a wafer 16 of suitable target material, such as tritium, that interacts with ions of the gas within the generator to produce particles such as neutrons. The entire interior of the housing may be filled with deuterium gas at a pressure of be tween 15 and 60 microns of mercury.

As shown more clearly in Fig. 2, a radio frequency coil 3 is positioned around the ionization compartment 2. The coil is connected to a suitable source of radio frequency energy 25 by electrical leads 31 and 33. For the purpose of providing an electric field for attracting ions out of the accelerating compartment 2 and toward target member 15, there is provided a pulsed voltage source 23 having output terminals 21 and 25. The pulsed voltage source 23 shouldbe capable of generating an electrical pulse train having a peak voltage in the vicinity of kilovolts. Preferably, each pulse generated by the pulse source comprises a first half cycle during which terminal 21 is negative with respect to terminal 25, followed by a second half cycle during which terminal 25 is negative with respect to terminal 21. Terminal 21 of the pulsed source 23 is connected to a conductive rod 17 that extends through housing vlxto support target member 15. Terminal 25 is connected to electrical lead .33 by means of capacitor 35 so that lead 33 is at ground potential insofar as alternating currents are concerned.

Capacitor 35 may be includedin the'radio frequency 7 source 29, if convenient, as the radio frequency source is also connected to terminal 25.

The plate that divides the generator into compartments 2 and 14 comprises a multiplicity "of 25- to ZOO-mesh glass balls. The balls are formed into aplate by placing them in a suitable form and heating them slightly above the annealing temperature so that the surfaces fuse together. The'manner in which the balls are :fused together is shown most perspicuously in Fig. 3. The balls need not be all of a' single size. The plates may, have .a. thickness between .08'to 0.13 inch; a very satisfactory size has beenifound to-be approximately inch. The

- plate may be fused to the lower end of neck 5 or, as

shown in Fig. 1, a small internal ridge 6 may be pro-- vided on which the plate may rest While the upper and lower portions of the housing are being fused together atthe point designated by the reference numeral 8. I

In operation, the radio frequency energy source 29 is energized to produce an ionized gas plasma in'the ionization compartment 2. When a voltage pulse is applied between the coil 3 and the target member 15, electric lines of force will tend to pass through the plasma, through the sintered glass plate 7, and through the accelerating gap 14. The lines of force will preferentially pass through the plasma rather than follow other paths because there is a substantial capacity between the coil and the plasma. Ions in the ionization compartment 2 are drawn. toward plate 7 along the electric lines of force. The majority of the ions will strike the surfaces of the glass balls and ricochet back into the ionization compartment,1and in so doing, will maintain the plasma. The accumulation of ions near the glassplate will build up a slight differential pressure across the plate. Some of the ions will find their way through the interstices between the glass balls to the ion accelerating compartment 14 and will be directed against the tritium-containing Wafer 16 in target member 15. The ion beam between the sintered glass partition 7 and the target will be very broad and uniformly distributed over the surface of the target. This is extremely advantageous in that localized heating of the target will be minimized and maximum use will be made of the tritium in the target for neutron generating purposes.

During the first half cycle of each voltage pulse applied between the coil 3 and target member 15, ions will bombard the target member so that neutrons and secondary electrons willbe emitted from the target insert 16. vThe secondary electrons will tend to collect on the sintered glass plate, enhancing the ion flow through the plate. During the second half cycle of each voltage pulse, the secondary electrons will return to the target member. Thus, there is practically no net flow of electrons; this reduces the amount of power drawn from source 23.

It should be emphasized that the voltage drop through the plasma in ionization compartment 2 will be relatively very small compared with the voltage gradient in accelerating gap 14. Therefore, the major portion of the voltage drop between coil 3 and the target member 15 will appear between the sintered glass plate 7 and the target member.

There is provided by the invention a very rugged, trouble-free radiation source. Inasmuch as there is only one mechanical connection to be made through the housing, the radiation source is mechanically very strong and sturdy. Localized heating of the target member is minimized by the invention and maximum use is made of the material in the target member for radiation generating purposes. The radiation source is adapted for pulsed operation and, therefore, is particularly suitable for use in connection with borehole logging techniques requiring pulse operation of a neutron source.

The invention is not to be restricted to the specific structural details, arrangement of parts, or circuit connections herein set forth, as various modifications thereof may be effected without departingfrom the spiritand scope of thisinvention, a

What is claimed is: r

1. A neutron generator comprising: a gas-tight envelope enclosing anionizable gas; radio frequency field producing means, includinga coil wound around a portion of said envelope, for producing a radio frequency electromagnetic field in said envelope adapted to interact with molecules of gas to produce an ionized gas plasma in said envelope; a target in said envelope out of the portion thereof about which said coil is wound, adapted to interact with ions from the ionized gas plasma toemit neutrons; :ayoltage pulse generator having first and sec- 0nd output terminals; circuit means connecting said first terminal to said radio frequency field producing means and said second terminal to said target so that said target is at a negative potential with respect to said coil for at least a portion of each voltage pulse from said pulse generator; and a partially ion-permeable sintered glass plate dividing said envelope into two compartments, one compartment including the'portion of said envelope about which said coil is wound, andthe other computment enclosing said ion target, said sintered glass plate having a multiplicity of small openings therethrough defining tortuous ion paths, and being adapted to confine the ionized gas plasma produced by said radio frequency field producing means to said one compartment and being suificientlyimpermeable to ions to permit said radio frequency field producing means to maintain said ion plasma when voltage pulses are applied between said coil and said ion target.

2. A radiation generator as defined in claim 1 whereinthe gas in the envelope is deuterium and the target contains tritium.

3. A neutron generator comprising: a gastight envelope enclosing an ionizable gas;'a coil wound about a portion of said envelope adapted to be energized by radio' frequency current, for producing a radio frequency el'ectromagneticfield in saidenvelope adapted to interact with molecules of gas to produce an ionized gas plasma in said envelope; an ion target in said envelope out of' the portion thereof about which said coil is wound, adapted to. interact with ions from the ionized gas plasma to emit neutrons; a voltage pulse generator having first and second output terminals adapted to produce output pulses at said terminals so that said first terminal is at a negative potential over at least a portion of each pulse; circuit means connecting said first terminal to said coil and said second terminal to said target; and a partially ionpermeable sintered glass plate dividing said envelope into two compartmentaone compartment including the portion of said envelope about which said coil is wound, and the other compartment enclosing said ion target, said sintered glass plate having a multiplicity of small openings therethrough defining tortuous ion paths, and being adapted to confine the ionized gas plasma produced by said coil to said one compartment, and being sufl'iciently impermeable to ions to permit said coil to maintain said ionized gas plasma when voltage pulses are applied between said coil and said ion target. a

4. A neutron generator comprising: a gastight envelope enclosing an ionizable gas; a sintered glass partition dividing said envelope into an ion generating compartment and an ion accelerating compartment, said sintered glass partition including a multiplicityof glass balls surface-fusedtogether to form a plate having a thickness between 0.08 inch and 0.13 inch through which ions may pass via the intersticesbetween the balls; an ion target in said ion accelerating compartment spaced from said partition, adapted to emit neutrons when stricken by ions from said ion generating compartment; a radio frequency field producing means, including a radio frequency coil around said ion generating compartment, adapted to produce a radio frequency field for producing an ionized gas plasma in said ion generating compartment; a source of high voltage pulses having first and second output terminals, adapted to produce output. pulses; and means connecting said first output terminal to said ion target, and corinecting said second terminal to said radio frequency C01 l 5. A' neutron generator comprising: a gas-tight envelope enclosing an ionizable gas; a sintered glass partiition dividing 'said envelope into an ion generating comsurface-fused. together to form aplate havinga thickness between 0.08 inch and 0.13 inch through which ions may pass via the. interstices between the balls, said glass balls having a diameter between 0.001 inch and 0.1 inch; an ion target in said ion accelerating compartment spaced from said partition, adapted to emit neutrons when stricken by ions from said ion generating compartment; a radio frequency field producing means, including a radio frequency coil around said ion generating compartment adapted to produce a radio frequency field for producing an ionized gas plasma in said ion generating compartment; a source of high voltage pulses having first and second output terminals, adapted to produce output pulses at said terminals so that said first terminal is negative with respect to said second terminal over at least a first portion of each pulse; and means connecting said first output terminal to said ion target, and connecting said second terminal to said radio frequency coil.

6. A neutron generator as defined in claim 5 wherein the gas in the envelope is deuterium and the target contains tritium.

7. In a neutron generator comprising a gas-tight envelope enclosing an ionizable gas, a radio frequency field producing means outside of said envelope and operatively positioned with respect to a first portion of the envelope to produce an ionized gas plasma within said first portion, and an ion target in a second portion of the envelope adapted to emit neutrons when voltage pulses of predetermined amplitude are placed between said radio fre quency field producing means and said target so that ions from the plasma strike said target with predetermined energy, the improvement comprising an ion-permeable sintered glass partition in said envelope separating said first portion from said second portion, said sintered glass partition having a multiplicity of openings therein defining tortuous ion paths through which a limited number of ions from the ion plasma may pass into the second portion of said envelope for acceleration to said target.

8. In a neutron generator comprising a gas-tight envelope enclosing an ionizable gas, a radio frequency field producing means outside of said envelope and operative- 1y positioned with respect to a first portion of the envelope to produce an ionized gas plasma within said first portion, and an ion target in a second portion of the envelope adapted to emit neutrons when voltage pulses of predetermined amplitude are placed between said radio frequency field producing means and said target so that ions from the plasma strike said target with predetermined energy, the improvement comprising an ion-permeable sintered glass partition in said envelope separating said first portion from said second portion, said sintered glass partition comprising a multiplicity of glass balls having diameters between .01 inch and .1 inch surface-fused together so as to form a plate having a thickness between .08 inch and .13 inch through which ions may pass into said second portion of the envelope via the interstices between the balls.

9. In a neutron generator comprising a gas-tight envelope enclosing an ionizable gas, a radio frequency field producing means outside of and operatively positioned with respect to a first portion of the envelope to produce an ionized gas plasma said first portion, and an ion target in a second portion of the envelope adapted to emit neutrons when voltage pulses of predetermined,

amplitude are placed between said radio frequency field producing means and said target so that ions from the plasma strike said target with predetermined energy, the impovement comprising an ion-permeable sintered glass partition in said envelope separating said first portion from said second portion, said sintered glass partition comprising a multiplicity of glass balls having diameters between .01 inch and .1 inch surface-fused together so that interstices are formed between the balls through which ions from the plasma may pass into the second portion of the envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,689,918 Youmans Sept. 21, 1954 2,786,156 Lorenz Mar. 19, 1957 2,831,134 Reifenschweiler Apr. 15, 1958 2,856,532 Martina Oct. 14, 1958 

